You can also share the cache between multiple Lookup transformations by using a persistent lookup cache and naming the cache files. You can share one cache between Lookup transformations in the same mapping or across mappings.
The Integration Service uses the following process to share a named lookup cache:
When the Integration Service processes the first Lookup transformation, it searches the cache directory for cache files with the same file name prefix.
If the Integration Service finds the cache files and you do not specify to recache from source, the Integration Service uses the saved cache files.
If the Integration Service does not find the cache files or if you specify to recache from source, the Integration Service builds the lookup cache using the database table.
The Integration Service saves the cache files to disk after it processes each target load order group.
The Integration Service uses the following rules to process the second Lookup transformation with the same cache file name prefix:
The Integration Service uses the memory cache if the transformations are in the same target load order group.
The Integration Service rebuilds the memory cache from the persisted files if the transformations are in different target load order groups.
The Integration Service rebuilds the cache from the database if you configure the transformation to recache from source and the first transformation is in a different target load order group.
If you do not configure the first Lookup transformation in a target load order group to recache from source, and you do configure the subsequent Lookup transformation to recache from source, the Integration Service does not rebuild the cache.
If the cache structures do not match, the Integration Service fails the session.
If you run two sessions simultaneously that share a lookup cache, the Integration Service uses the following rules to share the cache files:
The Integration Service processes multiple sessions simultaneously when the Lookup transformations only need to read the cache files.
The Integration Service fails the session if one session updates a cache file while another session attempts to read or update the cache file. For example, Lookup transformations update the cache file if they are configured to use a dynamic cache or recache from source.